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                [Usaco2006 Feb]Stall Reservations 专用牛棚                </h1>
                <p>时间限制：10s&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;  空间限制：64MB</p>			</div>
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                                <h3>题目描述</h3><p><p><span style="font-size: medium; ">Oh those picky N (1 &lt;= N &lt;= 50,000) cows! They are so picky that each one will only be milked over some precise time interval A..B (1 &lt;= A &lt;= B &lt;= 1,000,000), which includes both times A and B.  Obviously, FJ must create a reservation system to determine which stall each cow can be assigned for her milking time. Of course, no cow will share such a private moment with other cows.  Help FJ by determining: * The minimum number of stalls required in the barn so that each   cow can have her private milking period * An assignment of cows to these stalls over time  </span></p>
<p><span style="font-size: medium; ">有N头牛,每头牛有个喝水时间,这段时间它将专用一个Stall 现在给出每头牛的喝水时间段,问至少要多少个Stall才能满足它们的要求</span></p></p><hr/><h3>输入格式</h3><p><p><span style="font-size: medium; ">* Line 1: A single integer, N </span></p>
<p><span style="font-size: medium; "> * Lines 2..N+1: Line i+1 describes cow i's milking interval with two         space-separated integers.</span></p></p><hr/><h3>输出格式</h3><p><p><span style="font-size: medium; ">* Line 1: The minimum number of stalls the barn must have.</span></p>
<p><span style="font-size: medium; ">  * Lines 2..N+1: Line i+1 describes the stall to which cow i will be         assigned for her milking period.</span></p></p><hr/><h3>样例输入</h3><pre>5
1 10
2 4
3 6
5 8
4 7
</pre><hr/><h3>样例输出</h3><pre>4


OUTPUT DETAILS:

Here's a graphical schedule for this output:

Time     1  2  3  4  5  6  7  8  9 10
Stall 1 c1>>>>>>>>>>>>>>>>>>>>>>>>>>>
Stall 2 .. c2>>>>>> c4>>>>>>>>> .. ..
Stall 3 .. .. c3>>>>>>>>> .. .. .. ..
Stall 4 .. .. .. c5>>>>>>>>> .. .. ..

Other outputs using the same number of stalls are possible.</pre><hr/><h3>提示</h3><p><p>不妨试下这个数据,对于按结束点SORT,再GREEDY的做法 1 3 5 7 6 9 10 11 8 12 4 13 正确的输出应该是3</p></p><hr/><h3>题目来源</h3><p>Silver</p>
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